During recent years, it has been possible to develop internal combustion engines towards an improved operation economy and a reduced environment affection by the introduction of digital control systems for optimization in different operative situations. For example, this is the case for fuel injection, ignition, variable compression and controllable valves.
During the powering of vehicles it is a problem that, in spite of said improvements during the recent years, the varying operative situations result in the average efficiency of the engines becoming low and the effect on the environment becoming large. There is a further problem as the varying operative situations also result in a varying composition of different poisons and pollutions of the exhaust gases, thereby making the filtering of exhaust gases difficult.
One example of a vehicle engine that is environment friendly is the hybrid engine that mainly operates at a constant number of revolutions per minute that is adapted to a predetermined generator. This engine operates as best when it performs the requested operation at the highest possible efficiency. As the load is constant, also the combustion can be set in order to, in combination with different techniques, result in the lowest possible content of pollutions and poisons in the exhaust gases, such as for example nitrogen oxides and hydrogen carbons, and, in certain cases, soot particles.
If internal combustion engines could meet a varying need of torque, which is the result of different operative situations, with the highest possible efficiency, from the lowest need to the uppermost need, important advantages as to operation economy and environment would be achieved. Such an engine would have the advantages of the hybrid engine in the different operative situations that may come in question for a vehicle. The free-piston engine, based on the idea of performing optimal power strokes upon need thereof, and only then, would be a solution to the above-mentioned problem. However, the free-piston engine in which the moment of the piston is controlled by means of hydraulics or pneumatics, has not become widely spread since there has not been developed a sufficiently good solution for controlling the piston during the compression stroke with subsequent combustion. Strongly accelerating increase of pressure at the end of the compression stroke, and an added, explosive increase of pressure during combustion, results in problems with controlling the movement of the piston at its upper dead point.
The present invention implements, to a high degree, the advantages of the free-piston engine, and solves the above mentioned problems.